Since showers, including hand held ones have flow restrictors in them, using them to fill the tub is not a good idea. But you can use a conventional filler with a transfer valve to operate the hand held unit.

: I am installing a whirlpool type tub and like the idea of having a personal shower to use for rinsing it out. Does anyone use these as the main tub fill faucet or is this a crazy idea? I was thinking of something like the new pull out kitchen faucets, but with a flow capacity appropriate for a tub.